Document encoders which are well known in the art typically fall into two general categories. The first category of encoders includes those encoders which utilize a step function to position the document to be encoded at a particular point. Such encoders function in a manner typically associated with typewriters or other mechanical printers and are not generally compatible with high speed document processors.
A second category of document encoders which is capable of encoding continuously moving documents is nonetheless incompatible with modern financial document processors. The second category of encoders includes laser printers and ink jet printers. While these two types of encoders are capable of encoding a moving document, the magnetic ink required for use with financial documents such as checks is incompatible with current ink jet technology.
It is known in the art to print across a document in horizontal motion, sometimes referred to as horizontal "on the fly" printing. Printing "on the fly" may be accomplished by providing a number of fixed hammers and a corresponding set of fixed character dies, through which a document and an ink ribbon are transported in unison while the hammers are activated to print a sequence of characters on the document. The printing of documents "on the fly" has been used with great success in the encoding of financial documents, such as checks, in high speed encoding systems such as the one shown in U.S. Pat. No. 4,492,161 issued to the assignee of the present application, the disclosure of which is incorporated herein by reference.
In the prior art "on the fly" financial document encoders, magnetic ink ribbons are used to encode the documents with magnetic characters. Such magnetic ink ribbons are typically single-strike ribbons, that is, the magnetic ink associated with each character is totally removed from the ribbon during the printing of that character, and the same section of ribbon cannot be used a second time. In the prior art encoders, the ribbon control mechanism provides for transport of the ribbon in one direction only, with the ribbon transport being activated to transport the ribbon in unison with a financial document in the apparatus by the sensing of the leading edge of the document just before the document enters the print zone between the hammers and die. Specifically, an optical sensor is provided to sense the leading edge of the document and is located directly adjacent the entrance to the print zone. The ribbon transport is then deactivated in the prior art mechanism when the encoding process on a document is finished.
The prior art ribbon transport is deactivated once the last character in a series of characters, in time, is struck. It will be understood from the disclosure of the assignee's aforementioned prior patent that the character physically located last in a series of characters on a document is not necessarily the last character to be struck in time. The chronological sequence of character strikes will be dependent not only on the position of the character on the document but also the position of the character on the die set. As a result, when the last character is struck, a gap of unspent ribbon remains in the die between the entrance to the print zone and the last character. This portion of unspent ribbon is not used in printing the next document to enter the print zone, because the ribbon transport will be activated as the next document enters the print zone.
The gaps of unspent ribbon between spent portions represents a substantial wastage of ribbon. At a typical wastage rate of 50%, the typical customer encoding one million documents per month could realize a substantial savings if the amount of ribbon wastage could be controlled, thus, a need presently exists for a ribbon control mechanism that eliminates the gaps of unspent ribbon in an "on the fly" printing apparatus.